Moving towards in situ tracheal regeneration: the bionic tissue engineered transplantation approach

Abstract

In June 2008, the world's first whole tissue-engineered organ - the windpipe - was successfully transplanted into a 31-year-old lady, and about 18 months following surgery she is leading a near normal life without immunosuppression. This outcome has been achieved by employing three groundbreaking technologies of regenerative medicine: (i) a donor trachea first decellularized using a detergent (without denaturing the collagenous matrix), (ii) the two main autologous tracheal cells, namely mesenchymal stem cell derived cartilage-like cells and epithelial respiratory cells and (iii) a specifically designed bioreactor that reseed, before implantation, the in vitro pre-expanded and pre-differentiated autologous cells on the desired surfaces of the decellularized matrix. Given the long-term safety, efficacy and efforts using such a conventional approach and the potential advantages of regenerative implants to make them available for anyone, we have investigated a novel alternative concept how to fully avoid in vitro cell replication, expansion and differentiation, use the human native site as micro-niche, potentiate the human body's site-specific response by adding boosting, permissive and recruitment impulses in full respect of sociological and regulatory prerequisites. This tissue-engineered approach and ongoing research in airway transplantation is reviewed and presented here.

Fig 1

Steps towards completely tissue-engineered human trachea. A human donor trachea (A), (B) was decellularized (C), readily re-colonisated with epithelial cells and MSC-derived chondrocytes (cultured from cells taken from the recipient [D]) via a dynamic bioreactor with internal rotation of the graft (E) and used to successfully replace patient’s left main bronchus.

Fig 2

Tracheal decellularization process and potential solution to possible technical problems.

Fig 3

After 25 cycles of the detergent-enzymatic treatment only few chondrocytes (A, ×50) and a mild immunoreactivity against HLA-DR, HLA-DP, HLA-DQ antigens (B; ×200) were still present. SEM micrographs revealed that the basal lamina was partially maintained on the luminal surface (C), whereas an irregular network of collagen fibres was present on the external one (D).

Fig 4

Rotational bioreactor developed for GMP processing and improved clinical handling and automation (A). Decellularized trachea, reseeded with MSCs, placed into the bioreactor (B), which allows simultaneous air and liquid perfusion and sterile handling (C).

Fig 5

Bionic concept towards worldwide tissue-engineered tracheal replacement. The retrieved human tracheas are kept at –4°C and can be stored up to 11 months. Operations can be made as an elective procedure and purely intraoperatively (eliminating the need of human cell transportation, manipulation): a bone marrow aspiration of 30 to 60 ml needs to be centrifugated and then seeded on the tracheal matrix, without any further cell manipulation (thereby it will not be a cell therapy nor and advanced therapy). The own patient’s stem cells can be activated, controlled and induced to differentiation and proliferation by means local and systemic recruitment, boosting, permissive and commitment factors.

Fig 6

The mRNA expression profile of the erythropoietin receptor and of the tissue protective submit of the erythropoietin receptor (β-CR) in different mouse tissues. GAPDH was used as a housekeeping gene (PCR).

Fig 7

Bionic tissue-engineering concept.